Chemical Mechanical Planarization Pad With Surface Characteristics

ABSTRACT

A polishing pad includes a polymer matrix and polyhedral oligomeric silsequioxane (“POSS”) molecules or soluble particles and a surfactant dispersed within the polymer matrix. A polishing pad can be formed by casting a liquid polymer on a conveyer belt having a casting surface with a set of projections and curing the liquid polymer on the conveyer belt such that a polymer matrix has a surface with a second set of projections complimentary to the first set of projections.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application Ser. No. 61/247,411, filed on Sep. 30, 2009, the entire disclosure of which is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to a chemical mechanical planarization pad.

BACKGROUND

An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer until the non-planar surface is exposed. For example, a conductive filler layer can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. The filler layer is then polished until the raised pattern of the insulative layer is exposed. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. In addition, planarization is needed to planarize the substrate surface for photolithography.

Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against the polishing surface of a polishing pad, such as a rotating polishing disk or linearly advancing belt. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, which can include abrasive particles, is supplied to the surface of the polishing pad, and the relative motion between the substrate and polishing pad results in planarization and polishing.

One objective of a chemical mechanical polishing process is to achieve wafer to wafer polishing uniformity. If different substrates are polished at different rates, it becomes difficult to achieve a uniform target layer thickness between multiple wafers. Another objective of a chemical mechanical polishing process is to achieve within wafer polishing uniformity. If different areas on the substrate are polished at different rates, then it is possible for some areas of the substrate to have too much material removed (“overpolishing”) or too little material removed (“underpolishing”), which can result in non-uniform topography across the substrate.

SUMMARY

In general, in one aspect, a polishing pad includes a polymer matrix and polyhedral oligomeric silsequioxane (“POSS”) molecules dispersed within the polymer matrix. This and other embodiments can optionally include one or more of the following features. The POSS molecules can be chemically linked to the polymer matrix. The POSS molecules can include a functional group, and wherein the functional group is selected from a group consisting of NH₂, OH, SH, R—NH, —NCO, and COOH. The polymer matrix can include polyurethane. The polymer matrix can be porous. The pores of the polymer matrix can be filled with a gas. The gas can be nitrogen. The pores can include 15-40% of the polishing pad by volume. The hardness of the polishing pad can be between approximately 40 and 75 Shore D. The POSS molecules can include approximately 5 to 15 percent of the polishing pad by weight.

In general, in one aspect, a method of making a polishing pad includes mixing a polymer solution and polyhedral oligomeric silsequioxane (“POSS”) molecules together to form a mix and curing the mix such that a polymer matrix having POSS particles is formed.

This and other embodiments can optionally include one or more of the following features. The polymer solution can include polyurethane. The method can further include bubbling gas through the mix prior to curing. The gas can include nitrogen.

In general, in one aspect, a polishing pad includes a polymer matrix, soluble particles dispersed within the polymer matrix, and a surfactant dispersed within the polymer matrix.

This and other embodiments can optionally include one or more of the following features. The polymer matrix can be porous. The soluble particles can be chosen from a group consisting of CaCO₃, K₂SO₄, phenolic novolac, and polyethylene glycol ether. The soluble particles can be approximately 1 to 25 micrometers in size. The soluble particles can include approximately 1 to 15% of the polishing pad by weight. The polymer matrix can include polyurethane. The surfactant can be chosen from a group consisting of copolymers, block copolymers, and nonionic surfactants. The hardness of the polishing pad can be between approximately 60 and 75 Shore D.

In general, in one aspect, a method of making a polishing pad includes casting a liquid polymer on a conveyer belt, wherein the conveyer belt comprises a casting surface with a first set of projections, and curing the liquid polymer on the conveyer belt such that a polymer matrix is formed, wherein the polymer matrix has a surface with a second set of projections, the second set of projections being complimentary to the first set of projections.

This and other embodiments can optionally include one or more of the following features. The method can further include injecting a gas through the liquid polymer prior to casting. The gas can be nitrogen. The casting surface of the conveyer belt can include a material chosen from a group consisting of stainless steel, Teflon, and silicone. The polymer can include polyurethane. The method can further include detaching the matrix from the conveyer belt.

Certain implementations may have one or more of the following advantages. Having POSS molecules dispersed within the polymer matrix can decrease pad wear by both making the polishing pad harder and increasing the lubrication of the surface of the polishing pad. Dispersing soluble particles within the polymer matrix can increase the polishing pad hardness, thereby reducing pad wear, and can increase surface roughness of the polishing pad, thereby increasing the removal rate of the polishing surface during CMP. Dispersing a surfactant within the polymer matrix can uniformly disperse the POSS and/or particles, thus also increasing surface roughness. Further, a pad as described herein can be made thicker than traditional pads because the polymer walls between the grooves are stronger and therefore are less likely to collapse. Curing liquid polymer on a mold having ridges can eliminate the need to put grooves in after curing, thereby saving money and time. Likewise, curing the liquid polymer on a mold having ridges can minimize pad to pad variation that can be caused by grooving knives if grooves are formed after curing.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a cross-section of a polishing pad having a polymer matrix.

FIG. 2 is a schematic of a cross-section of a polishing pad having nanoparticles dispersed throughout a polymer matrix.

FIG. 3 is a schematic of a cross-section of a polishing pad having soluble particles dispersed throughout a polymer matrix.

FIG. 4 is a schematic of a system for creating air bubbles in a liquid polymer mix.

FIG. 5A is a schematic of a system for curing a liquid polymer mix over a substrate.

FIG. 5B is a schematic showing a close-up of a grooved substrate for curing a liquid polymer mix.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

During chemical mechanical polishing, a lack of surface roughness of the polishing surface of the polishing pad can result in a low removal rate. Furthermore, polishing pads can have a high wear rate, causing short pad life and requiring frequent replacement of the polishing pads. Polishing pad surface roughness can be increased by dispersing soluble particles and/or surfactant within the polishing pad. Likewise, the wear rate of the polishing pad can be reduced by dispersing molecules, e.g., nanoparticles, that increase the hardness of the pad material, such as polyhedral oligomeric silsequioxane (“POSS”) molecules, and/or soluble particles within the polishing pad.

Referring to FIG. 1, a polishing pad 100 can include a polishing surface 101 and a matrix 102. The matrix 102 can be a polymer matrix, for example, a polyurethane, nylon, expoxy, or poly(methyl methacrylate) (PMMA) matrix. The matrix 102 can include pores 104. The pores 104 can be approximately 15-60 μm, such as 19-50 μm in diameter and approximately 15-40% of the total volume of the polishing pad 100. The pores 104 can be filled with a gas, e.g. substantially pure nitrogen.

In one implementation, shown in FIG. 2, nanoparticles 202 can be incorporated into matrix 102. The nanoparticles can be dispersed homogeneously through the polishing pad. As an example, the nanoparticles 202 can be, for example, particles of polyhedral oligomeric silsequioxane (“POSS”). The functional group in the POSS can be, for example, OH, NH₂, COOH, R—NH, SH, or —NCO, and can chemically bond to matrix 102. Thus, for example, the functional groups of POSS nanoparticles can cross-link with polyurethane in the matrix 102. The nanoparticles 202, e.g. POSS particles, can have a diameter of approximately 5-20 nm, such as 5-10 nm, at the molecular level. As another example, the nanoparticles 202 can be inorganic or organic nanoparticles, such as colloidal silicon nanoparticles. Such nanoparticles 202 need not be chemically bonded to the matrix 102, but may be physically bonded to the matrix 102 instead. The nanoparticles 202 can make up approximately 5-15% of the polishing pad 100 by weight. The incorporation of nanoparticles 202 into the polishing pad 100 can increase the hardness of the polishing pad 100 to, for example, 40-75 Shore D.

In another implementation, shown in FIG. 3, soluble particles 302 can be incorporated into the matrix 102. The soluble particles 302 can be organic or inorganic particles, such as CaCO₃, K₂SO₄, phenolic novolac, or polyethylene glycol ether and can measure between approximately 1 μm and 10 μm in diameter. The soluble particles 302 can be dispersed homogeneously through the polishing layer and can make up approximately 1-15%, such as 1-5%, of the polishing pad by weight. The soluble particles 302 on the polishing surface of polishing pad 100 can dissolve when contacted with polishing liquid during the CMP process, leaving further recesses or pits in the polishing surface and thereby enhancing the surface roughness of the polishing pad 100. The incorporation of soluble particles 302 can increase the surface roughness of the polishing pad 100 when the soluble particles 302 on the surface dissolve. The incorporation of soluble particles 302 can also increase the hardness of the polishing pad 100 to, for example, 60-75 shore D, such as 62-70 shore D.

Further, a surfactant can be included in the polymer matrix, which, as discussed below, can increase the surface roughness of the pad 100. The surfactant can be, for example, a copolymer, block copolymer, or nonionic surfactant.

Referring to FIG. 4, a polishing pad 100 is manufactured by stirring a liquid polymer mix 402 with a mixer 404 in a vat 406. Gas 408, e.g. substantially pure nitrogen gas, is injected into the liquid polymer mix 402 to create bubbles 410. Some of the bubbles 410 remain in the liquid polymer mix 402 to create pores 104 in the cured polishing pad 100 (see FIGS. 1-3). In some implementations, nanoparticles 202 are added to the liquid polymer mix 402 in the vat 406 such that nanoparticles will be incorporated into the polishing pad 100. Likewise, in other implementations, soluble particles 302 are added to the liquid polymer mix 402 in vat 406 such that the soluble particles will be incorporated into the polishing pad 100. Moreover, in some implementations, a surfactant is added to the liquid polymer mix 402 in the vat 406 to stabilize the bubbles 410, nanoparticles, and/or the soluble particles 302.

After mixing, the contents of the vat 406 can be poured through an ejector 502 over a mold 504, as shown in FIG. 5A. The mold 504 can be a conveyor belt and can continuously move, e.g. on rollers 506, such that a sheet 508 of liquid polymer mix 402 is formed on top of the mold 504. The sheet 508 can then be allowed to cure over the mold 504. As shown in FIG. 5B, the mold 504 can have projections, e.g. ridges 510, along its top surface such that a complimentary set of ridges 512 is formed in the bottom surface of the sheet 508 as the sheet 508 cures. The ridges 510 can be in the shape, for example, of concentric circles, a rectangular grid (sometimes called an “XY pattern”), or spirals along the top surface of the substrate 504, so that the complimentary set of ridges 512 are also concentric circles, an XY pattern, or spirals.

Although not shown, once the sheet 508 has cured, a stamp can cut individual polishing pads 100 from the sheet 508. The polishing pads 100 can then be removed from the substrate 504. The substrate 504 can be made of, for example, stainless steel, a Teflon material, a silicone material, or a material coated with Teflon or silicon such that the polishing pads 100 can be easily removed from the substrate 504 after curing. The polishing pad 508 can then be placed in a CMP apparatus (not shown) for CMP polishing.

The properties of a polishing pad can affect the polishing rate of a substrate during CMP. For example, large, poorly distributed pores (as opposed to evenly spaced small pores) in the polishing pad can reduce the surface roughness of the polishing pad. Reduced surface roughness, in turn, can decrease the polishing rate by reducing polishing liquid transport during polishing and decreasing the abrasiveness of the pad. By introducing soluble particles during the production of the polishing pad, the polishing rate can be increased, as before the soluble particles on the polishing surface dissolve, they can act as abrasives, and after the soluble particles on the polishing surface dissolve, the surface roughness can be increased due to small voids left behind. Furthermore, the introduction of surfactants to the formulation can increase the polishing rate by allowing for better distribution of voids, POSS nanoparticles, or soluble particles, and can thereby increase the surface roughness.

The polishing rate can be further increased by incorporating macro-texture or grooves into the surface of the polishing pad, which can facilitate the transport of polishing liquid during polishing. However, the creation of macro-texture after curing of the polishing pad can be extremely timely and expensive. By casting the precursor polishing pad mixture onto a substrate with grooves, the pad grooves can be generated during curing, thereby reducing the cost of creating grooves after curing.

The properties of the polishing pad can also affect the wear rate of the pad itself. In particular, if a polishing pad has high porosity, the wear rate of the pad can be high. By incorporating molecular level POSS into the polishing pad, the hardness of the pad can be increased, and the surface friction can be reduced, both of which can reduce the polishing pad wear rate. Likewise, the polishing pad wear rate can be reduced by incorporating soluble organic or inorganic particles into the polishing pad, which can increase the hardness of the polishing pad.

Particular embodiments of the invention have been described. Other embodiments are within the scope of the following claims. 

1. A polishing pad comprising: a polymer matrix; and polyhedral oligomeric silsequioxane (“POSS”) molecules dispersed within the polymer matrix.
 2. The polishing pad of claim 1, wherein the POSS molecules are chemically linked to the polymer matrix.
 3. The polishing pad of claim 1, wherein the POSS molecules include a functional group, and wherein the functional group is selected from a group consisting of NH₂, OH, SH, R—NH, —NCO, and COOH.
 4. The polishing pad of claim 1, wherein the polymer matrix comprises polyurethane.
 5. The polishing pad of claim 1, wherein the polymer matrix is porous.
 6. The polishing pad of claim 5, wherein the pores of the polymer matrix are filled with a gas.
 7. The polishing pad of claim 5, wherein the pores of the polymer matrix comprise 15-40% of the polishing pad by volume.
 8. The polishing pad of claim 1, wherein the hardness of the polishing pad is between approximately 40 and 75 Shore D.
 9. The polishing pad of claim 1, wherein the POSS molecules comprise approximately 5 to 15 percent of the polishing pad by weight.
 10. A method of making a polishing pad comprising: mixing a polymer solution and polyhedral oligomeric silsequioxane (“POSS”) molecules together to form a mix; and curing the mix such that a polymer matrix having POSS particles is formed.
 11. The method of claim 10, wherein the polymer solution comprises polyurethane.
 12. The method of claim 10, further comprising bubbling gas through the mix prior to curing.
 13. A polishing pad comprising: a polymer matrix; soluble particles dispersed within the polymer matrix; and a surfactant dispersed within the polymer matrix.
 14. The polishing pad of claim 13, wherein the polymer matrix is porous.
 15. The polishing pad of claim 13, wherein the soluble particles are chosen from a group consisting of CaCO₃, K₂SO₄, phenolic novolac, and polyethylene glycol ether.
 16. The polishing pad of claim 13, wherein the soluble particles are approximately 1 to 25 micrometers in size.
 17. The polishing pad of claim 13, wherein the soluble particles comprise approximately 1 to 15% of the polishing pad by weight.
 18. The polishing pad of claim 13, wherein the polymer matrix comprises polyurethane.
 19. The polishing pad of claim 13, wherein the surfactant is chosen from a group consisting of copolymers, block copolymers, and nonionic surfactants.
 20. The polishing pad of claim 15, wherein the hardness of the polishing pad is between approximately 60 and 75 Shore D.
 21. A method of making a polishing pad comprising: casting a liquid polymer on a conveyer belt, wherein the conveyer belt comprises a casting surface with a first set of projections; and curing the liquid polymer on the conveyer belt such that a polymer matrix is formed, wherein the polymer matrix has a surface with a second set of projections, the second set of projections being complimentary to the first set of projections.
 22. The method of claim 21, further comprising injecting a gas through the liquid polymer prior to casting.
 23. The method of claim 21, wherein the casting surface of the conveyer belt comprises a material chosen from a group consisting of stainless steel, Teflon, and silicone.
 24. The method of claim 21, wherein the polymer comprises polyurethane. 